1. Field of the Invention
The present invention relates to a cooling device utilizing a heat radiation member, such as a heat sink, so as to promote heat radiation from a target member such as an electronic component.
2. Description of the Prior Art
As disclosed in Japanese Patent Publication P2000-22059A, a heat sink is conventionally utilized to cool an electronic component mounted on a printed circuit board, for example. When the heat sink is received on the electronic component, a flat opposed surface of the heat sink is allowed to contact the upper surface of the electronic component. The heat sink should contact the upper surface of the electronic component over a larger area. The heat sink is thus urged against the upper surface of the electronic component. A biasing force from a spring is, for example, utilized to urge the heat sink against the electronic component.
If the heat sink is excessively urged against the electronic component, a larger stress is induced within the electronic component. Continuous application of the excessive urging force may cause deformation of the electronic component. Prevention of the stress or deformation in the electronic component is supposed to contribute to a reliable electric connection between the electronic component and the printed circuit board as well as a longer lifetime of the electronic component and the printed circuit board. It is preferable to reduce to the utmost any external force acting on the electronic component.
It is accordingly an object of the present invention to provide a cooling device capable of keep contacting a heat radiation member on the surface of a target member over a larger area with the smallest urging force.
According to a first aspect of the present invention, there is provided a cooling device comprising: a heat radiation member received on the surface of a target member at the opposed surface of the heat radiation member; a heat conductive fluid interposed between the surface of the target member and the opposed surface of the heat radiation member; and a slippage prevention mechanism restraining slippage of the heat radiation member along the surface of the target member.
In addition, according to a second aspect of the present invention, there is provided a cooling device comprising: a heat conductive fluid spreading over the surface of a target member; a heat radiation member disposed on the heat conductive fluid and urged against the surface of the target member with the atmospheric pressure; and a slippage prevention mechanism restraining slippage of the heat radiation member along the surface of the target member.
The heat conductive fluid serves to enhance the contact between the surface of the target member and the opposed surface of the heat radiation member. Even if a larger roughness or rough flatness is established on the surface of the target member or/and the opposed surface of the heat radiation member, the heat radiation member is allowed to contact the target member uniformly over a larger area. A higher heat conductivity can thus be established between the target member and the heat radiation member. Heat of the target member is efficiently transferred to the heat radiation member. Heat radiation from the heat radiation member can be promoted.
Moreover, the heat conductive fluid exhibits a property of adsorption between a pair of surfaces based on the fluidity of the heat conductive fluid itself. Although the adsorption allows the slippage of the heat radiation member along the surface of the target member, the adsorption reliably restrains the heat radiation member from moving in the perpendicular direction perpendicular to the surface of the target member. Specifically, the heat conductive fluid serves to prevent the heat radiation member from peeling off from the target member.
On the other hand, the slippage prevention mechanism serves to restrain slippage of the heat radiation member. The relative movement of the heat radiation member can be restrained along the surface of the target member, irrespective of inclination of the surface or vibration of the target member. The heat conductive fluid can be maintained enough between the heat radiation member and the target member over an enough extent irrespective of the slippage of the heat radiation member. The heat conductive fluid keeps the adsorption acting between the surface of the target member and the opposed surface of the heat radiation member.
In the above-described cooling device, as long as the slippage of the heat radiation member is restrained within a predetermined range, the heat conductive fluid solely serves to keep the heat radiation member on the surface of the target member. The atmospheric pressure solely acts on the heat radiation member so as to urge the heat radiation member against the surface of the target member. No excessive urging force may be applied to the target member.
The slippage prevention mechanism may preferably comprise a frame member surrounding the target member and the heat radiation member. The frame member should be designed to move relative to the target member and the heat radiation member along the perpendicular direction perpendicular to the surface of the target member. The frame member of this type can easily be attached to and detached from the heat radiation member. When the frame member is removed, the heat radiation member may be allowed to slip along the surface of the target member. The heat radiation member is easily allowed to take off from the target member in this manner. This leads to an easier detachment of the heat radiation member from the target member.
Alternatively, the slippage prevention mechanism may include a protrusion formed on the target member so as to engage the heat radiation member when the heat radiation member slips along the surface of the target member, or a protrusion formed on the heat radiation member so as to engage the target member when the heat radiation member slips along the surface of the target member. Otherwise, the cooling device may further include, in place of the aforementioned protrusions, a support member fixedly supporting the target member, and a protrusion fixedly located on the support member and engaging the heat radiation member when the heat radiation member slips along the surface of the target member.
The heat conductive fluid may include at least either of ceramic particles or metallic particles, as a filler, so as to establish the property of heat conductivity. Since the ceramic and metallic particles have a higher heat conductivity, the fluid is allowed to have a higher heat conductivity.
The heat conductive fluid may include a silicone grease as a solvent, for example. The silicone grease may keep its fluidity for a longer period of time irrespective of variation in temperature. Even if the target member gets heated, the fluidity of the heat conductive fluid can be maintained for a longer period of time. The heat radiation member can reliably be held on the target member for a longer time of period.
The aforementioned slippage prevention mechanism may allow the slippage of the heat radiation member along the surface of the target member within a regulated extent. In general, when the target member gets heated, a relative displacement is generated between the surface of the target member and the opposed surface of the heat radiation member in the lateral direction based on the difference in thermal expansion. The heat conductive fluid easily absorbs the relative displacement based on the fluidity itself. Moreover, since spaces are defined to allow the slippage of the heat radiation member within the regulated extent in the slippage prevention mechanism, the target member, the heat radiation member and the slippage prevention mechanism are reliably prevented from generation of internal stresses even if the target member and/or the heat radiation member thermally expand.
The heat radiation member may be a heat sink, for example. The heat sink may include a heat receiving plate received on the surface of the target member, and fins standing on the heat receiving plate in the vertical direction. The cooling device of this type may be utilized to cool an electronic component mounted on a printed wiring board or substrate.